An ultrafine particle film forming method and an ultrafine particle film forming system are described in Patent Document 1. This system is configured such that an ultrafine particle film is formed on a substrate by generating vapor atoms from a material and moving the vapor atoms through a carrying pipe together with inert gas. In other words, the configuration of such particle film forming system and method are expressed in general as follows: Upper and lower chambers are installed so as to communicate with each other by a narrow pipe. Then, the upper chamber is vacuumed, and coolant gas is made to flow into the lower chamber. Then, the vapor atoms evaporated from the metal material are cooled and moved into the upper chamber by the pressure difference between the upper and lower chambers. Then, the vapor atoms are collected, in a state of particles, on the substrate arranged in the upper chamber. The coolant gas is, for example, helium gas or argon gas and is made to flow so as to prevent aggregation and grain growth of the particles during the movement.
However, such a conventional particle film forming system has only been capable of depositing particles on the substrate. Therefore, for example, in the case where a hydrogen sensor is formed by using, as particles, Mg, a Mg—Ni alloy, or the like, which absorbs and stores hydrogen, the diffusion property of hydrogen (permeability of gas) becomes poor, so that the nylon-based resin is lowered. Further, in the case where such conventional particle film forming system is used for metal nanoparticles, when the metal nanoparticles are deposited on the substrate, the metal nanoparticles re-aggregate, so that the fine nanoparticle state of the metal nanoparticles cannot be maintained.